The field of the invention relates to the removal of mercury from liquid and gaseous fluids, particularly hydrocarbon oils.
Typical crude oils may contain about 0.5 to 10 ppb of mercury. Higher levels of mercury are often found in hydrocarbon condensates from natural gas production. Concentrations between fifty and three hundred parts per billion are present in the condensate from some fields.
High levels of mercury in hydrocarbon liquid, crude oil and condensate can cause problems in processing due to the corrosive effect of mercury on vital equipment such as cryogenic heat exchangers. Such heat exchangers are often made from aluminum which forms an amalgam with mercury. In addition, mercury in hydrocarbon products is released into the air upon combustion and causes environmental concerns.
A number of methods have been developed for removing mercury from gases and liquids. U.S. Pat. Nos. 4,094,777, 4,101,631, 4,419,107 and French Publication No. 2 310 795 disclose several such methods. The '777 patent and the French publication both employ a metal or metal compound supported by an adsorbent mass such as alumina or silica-alumina. The '777 patent teaches the use of copper sulphide within the mass while the French publication indicates that the preferred metals are silver or a mixture of silver with gold, nickel or copper. The French patent also teaches an optimum temperature range between -50.degree. and 200.degree. depending upon the nature of the active metal. The '631 patent discloses a process including passing a mercury-containing gas stream through a sorption zone containing a crystalline zeolitic molecular sieve having elemental sulfur loaded thereon.
The heavy condensate produced from some fields contains about twenty percent of C.sub.10 and higher hydrocarbons, and five percent of C.sub.20 and higher hydrocarbons. Typical crudes which often contain mercury are much heavier than the condensate, and can contain up to eighty percent C.sub.20 and higher hydrocarbons. When adsorbents are used to adsorb mercury directly, the non-selective adsorption of the heavy material competes too favorably with the mercury leading to low mercury adsorption capacity.